1. Field of the Invention
The present invention relates to an automatic analyzer which performs qualitative and quantitative analysis of biogenic substances such as blood, urine, etc. More particularly, the present invention relates to an automatic analyzer having a pipetting device including a nozzle for suctioning and discharging a sample, a syringe, a pipe, and a pressure sensor for monitoring the pressure in the pipe.
2. Description of the Related Art
Automatic analyzers in general pipette a sample such as blood, urine, cerebrospinal fluid, etc. from a test tube or a certain vessel for that purpose to a reaction vessel, mix the sample with a reagent to cause a reaction between the sample and reagent, and measure components contained in the sample by use of measurement means such as a photometer.
During sample pipetting, the nozzle of the pipetting device is inserted into the sample in the test tube or dedicated vessel, and the syringe is driven to pipette a particular amount of the sample, which amount is predetermined and stored in a calculation unit on a measurement-item-by-item basis.
Pipetting devices of recent automatic analyzers commonly detect the liquid surface of a sample by capacitance variation, stops the lowering operation of the nozzle immediately after it is inserted into the liquid surface, and sucks the sample. Since a biological sample having viscosity is commonly used as a sample, handling or storing it in the wrong way may cause air bubbles on its liquid surface. These air bubbles may cause incorrect detection of the liquid surface.
In this case, air may be sucked together with the sample, and an expected amount of the sample may not be sucked.
If the sample is measured while the expected amount of the sample cannot be sucked because of incorrect detection of the liquid surface, correct measurement results may not be obtained. As means for avoiding this, a technique disclosed in patent literature, JP-A-10-227799, provides two pressure sensors at different positions (one in the vicinity of the nozzle and the other in the vicinity of a pump) to detect sucked air based on the difference in pressure fluctuation between the two positions.